Airway epithelial cell death and inflammation are pathological features of chronic obstructive pulmonary disease (COPD). Mechanistic target of rapamycin (MTOR) is involved in inflammation and multiple cellular processes, e.g., autophagy and apoptosis, but little is known about its function in COPD pathogenesis. In this article, we illustrate how MTOR regulates cigarette smoke (CS)-induced cell death, airway inflammation, and emphysema. Expression of MTOR was significantly decreased and its suppressive signaling protein, tuberous sclerosis 2 (TSC2), was increased in the airway epithelium of human COPD and in mouse lungs with chronic CS exposure. In human bronchial epithelial cells, CS extract (CSE) activated TSC2, inhibited MTOR, and induced autophagy. The TSC2-MTOR axis orchestrated CSE-induced autophagy, apoptosis, and necroptosis in human bronchial epithelial cells; all of which cooperatively regulated CSE-induced inflammatory cytokines IL-6 and IL-8 through the NF-κB pathway. Mice with a specific knockdown of in bronchial or alveolar epithelial cells exhibited significantly augmented airway inflammation and airspace enlargement in response to CS exposure, accompanied with enhanced levels of autophagy, apoptosis, and necroptosis in the lungs. Taken together, these data demonstrate that MTOR suppresses CS-induced inflammation and emphysema-likely through modulation of autophagy, apoptosis, and necroptosis-and thus suggest that activation of MTOR may represent a novel therapeutic strategy for COPD.

Mucus hypersecretion is a common pathological feature of chronic airway inflammatory diseases including chronic obstructive pulmonary disease (COPD). However, the molecular basis for this condition remains incompletely understood. We have previously demonstrated a critical role of autophagy in COPD pathogenesis through mediating apoptosis of lung epithelial cells. In this study, we aimed to investigate the function of autophagy as well as its upstream and downstream signals in cigarette smoke-induced mucus production in human bronchial epithelial (HBE) cells and in mouse airways. Cigarette smoke extract (CSE), as well as the classical autophagy inducers starvation or Torin-1, significantly triggered MUC5AC expression, and inhibition of autophagy markedly attenuated CSE-induced mucus production. The CSE-induced autophagy was mediated by mitochondrial reactive oxygen species (mitoROS), which regulated mucin expression through the JNK and activator protein-1 pathway. Epidermal growth factor receptor (EGFR) was also required for CSE-induced MUC5AC in HBE cells, but it exerted inconsiderable effects on the autophagy-JNK signaling cascade. Airways of mice with dysfunctional autophagy-related genes displayed a markedly reduced number of goblet cells and attenuated levels of Muc5ac in response to cigarette smoke exposure. These results altogether suggest that mitoROS-dependent autophagy is essential for cigarette smoke-induced mucus hyperproduction in airway epithelial cells, and reemphasize autophagy inhibition as a novel therapeutic strategy for chronic airway diseases.

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b-defensin 2 (BD-2), an antimicrobial peptide, participates in airway defence. Cigarette smoke (CS) is a major risk factor for the development of chronic obstructive pulmonary disease. This study mainly aims to investigate the effect of CS on rat BD-2 (rBD-2) expression in rat airways.Rats were exposed to CS and treated with caffeic acid phenethyl ester (CAPE), a nuclear factor (NF)-kB inhibitor, or astragaloside IV (AS-IV), an active ingredient of Astragalus mongholicus. Besides the analysis of bronchoalveolar lavage fluid (BALF) and histological changes after CS exposure, rBD-2 expression was investigated with immunohistochemistry, reverse transcription PCR and ELISA. Total glutathione and nitric oxide (NO) levels in rat lungs were also detected.CS exposure markedly increased rBD-2 immunoreactivity, as well as rBD-2 mRNA and protein levels in rat airways, which were inhibited by CAPE treatment. Moreover, associated airway inflammation induced by CS was demonstrated by histological changes, increased cell counts and pro-inflammatory cytokines in BALF, and NF-kB activation and high levels of total glutathione and NO, which were all reversed by AS-IV in a dose-dependent fashion.In conclusion, CS exposure induces rBD-2 expression in rat airways via a NF-kB-dependent pathway, and AS-IV attenuates CS-induced airway inflammation due to its anti-inflammatory and antioxidant properties, at least partly through NF-kB inactivation.

The loss of alveolar structure and airspace enlargement are major pathological changes in chronic obstructive pulmonary disease (COPD). Type II alveolar epithelial cells (AECII) are involved in maintaining lung tissue repair and alveolar homeostasis. Long non‑coding RNAs (lncRNAs) are involved in multi‑regulating gene transcription, affecting processes including embryonic development, cell differentiation and cellular senescence. The primary aim of the present study was to explore the mechanisms of AECII senescence regulated by lncRNA‑mediated sirtuin 1 (SIRT1) and forkhead box O 3a (FoxO3a) signaling pathways in patients with COPD. Lung tissues from patients with COPD exhibited pathological characteristics and significantly increased senescence‑associated β‑galactosidase activity. Furthermore, the expression levels of senescence‑associated lncRNA1 (SAL‑RNA1), SIRT1 and FoxO3a were reduced, but SAL‑RNA2, SAL‑RNA3, p53 and p21 were upregulated in the lung tissues of patients with COPD compared with control. The results of the present study indicated that lncRNA‑mediated SIRT1/p53 and FoxO3a signaling pathways may regulate AECII senescence in the pathogenesis of COPD, which may provide a novel experimental basis for the treatment of COPD.